This invention relates to a fluid leakage detection system in a drain line. More particularly, the present invention integrates a commercially available finger push valve into a seal cavity leakage detection system placed inside an enclosed compartment, such as an aircraft engine or industrial machinery, providing a low-cost, non-intrusive means of early leak detection in a new or retrofit design. The method and apparatus disclosed in the present application provides an environmentally friendly alternative to other leak detection methods and improves reliability and maintainability.
Multi-joint hydraulic systems may have many fittings, which are not readily visible and thus are difficult to inspect on a routine basis. Sometimes minor leakage at such joints are not a problem for operations, therefore routine inspection is not necessary. In other applications, however, such as aerospace, high speed machinery, and transportation equipment, early leakage detection can be critical for operational and personnel safety. Quantifying leakage and leakage rate is necessary in order to distinguish between conditions which are allowable and those which are indicative of accelerated deterioration of a mechanical system. Therefore, a reliable, accurate, and fast determination of hydraulic system leakage can identify the need for maintenance and greatly improve prevention of catastrophic failures during operations.
Hidden-joints, while not visually accessible, are conventionally inspected by use of such devices as inspection mirrors. However, such efforts are subjective and non-quantitative. Often, visual inspection is not possible due to the compactness of the enclosed compartment and/or lighting conditions in the area of interest. Moreover, when portions of such hydraulic systems are thermally insulated, indirect observation is not possible and leak detection becomes a difficult, time-consuming, and critical task.
For environmental reasons, there is now a requirement that no engine fluids be expelled onto airport ramps. All such fluids, regardless of leakage source, must be collected, disposed of, or burned in the engine exhaust. Many gas turbine engines include an extensive drain system for transfer of fluid leakage to an interim storage area or reservoir outside the engine compartment. The storage area or reservoir provides a means for leakage detection. For example, one of the fluids that is expelled from an engine is leakage from an accessory drive seal. Before collector tanks were installed, fluid from a leaking seal cavity was routed to an overboard drain and could be observed dripping from the aircraft. That is the source of the term xe2x80x9cwitness drainxe2x80x9d. In such situations, technicians would note existence of the leak and would schedule corrective action to replace the leaking accessory seal. When collector tanks are used to capture the leaking fluid, there is no observable evidence to indicate that a seal is leaking, and the seal may continue to deteriorate until excessive oil loss is noted or other more serious operational symptoms develop. The problem is further complicated, for example, when collector tank drain lines are connected to a plurality of possible sources of joint and seal leakage. Typically, such drain lines are installed near oil, hydraulic or fuel seal points adjacent to moving elements, such as near gearboxes where other components are coupled to the engine via shafts passing through the gearbox housing. Other sources of leakage can be hydraulic actuators and fuel driven valves.
Traditionally, drain mast assemblies are installed in engines to satisfy the operational needs described above. Such drain systems provide an indication of leakage from a source to which the drain is connected but no indication as to the quantity or leakage rate of that source. In most commercial engine applications, operational drains drain away liquids that might accumulate during operation, and service drains collect liquids for removal during maintenance. Leakage associated with such service drains can be determined during maintenance by measuring the quantity of liquid collected. Typically, there are many drain lines feeding into the drain mast assembly, and for that reason, it is difficult to determine which particular drain line is leaking since the fluids tend to run onto adjacent drain lines. This disadvantage creates a problem for troubleshooting a leaking drain, and requires a time consuming investigation inside the nacelle and cowl assembly.
Prior art, U.S. Pat. No. 5,285,636, discloses an improved drain mast assembly having a plurality of collection chambers with each of the chambers coupled in liquid receiving relationship with a respective liquid drain line. The assembly allows identifications of individual drain lines having relatively high drain-rates. Each chamber in the improved assembly may include a transparent view window for visually determining the volume of liquid collected by the chamber. The valve in each chamber also includes a standpipe extending a pre-selected distance into the chamber for overflow draining of the chamber when the collected liquid exceeds a predetermined volume.
This patent essentially discloses a drain mast using a traditional overboard method to dispose of the leakage waste fluids. Once the drain mast fluid leak detection collection chamber is filled, the fluid is expelled from the aircraft. The system requires that the valve and standpipe be integrated within a compact space. This is to avoid creating an excessively large drain mast causing aerodynamic drag for the aircraft. The standpipe height determines the volume of the fluid retained in the detection chamber before being drained overboard, thus significantly complicating the design. Since the system focuses on use of the drain mast concept and is located outside the engine cowling, there is a resulting requirement to incorporate special design features, such as mountings, that must take aerodynamic effects into consideration. This makes the system expensive, heavy, difficult to maintain, and not retrofitable.
Therefore, there is a need for a cost-effective, accurate, safe, reliable, and efficient witness drain system, using commercially available components, to meet regulatory and environmental considerations and to allow for inspection and quantification of drain line leakage.
The present invention provides an apparatus and method to conveniently and accurately checks drain line leakage. The apparatus and method disclosed is lightweight, usable for both new and retrofit designs, inexpensive, and does not affect aerodynamic drag.
In one aspect of the present invention, a commercially available finger push valve is integrated into a witness drain valve system allowing excessive fluid in a drain line to continue along its original route. Disclosed is an apparatus comprised of a witness drain valve having a small built in reservoir that retains a small, predetermined portion of leaking fluid along the drain line. The apparatus can be installed in the drain line between the seal cavity and the environmental collector tank. As the fluid passes the leaking seal to the collector tank, a small sample is captured in the apparatus. Once the reservoir of the apparatus is full, the leaking fluid flows on to the collector tank as intended. The apparatus is non-intrusive and provides critical leakage information to engine maintenance crews. No standpipe is required nor is there a need for an overboard drain to dispose of waste fluid.
In another aspect of the present invention, a method of improving engine reliability and maintainability is disclosed. The method comprises the steps of: installing an improved witness drain valve having variable diameters along the fluid flow path to create a small reservoir of pre-designed volume appending the drain line; disposing the drain witness valve between the leaking seal and environmental collector tank; flowing fluid along the drain line; collecting a leakage fluid sample; inspecting leakage fluid amount through a commercially available finger push valve connected to the witness drain valve perpendicular to the flow direction; determining the need for maintenance of the seal; and scheduling maintenance as required before further seal deterioration occurs. The pre-designed volume may be determined during the design phase by calculating allowable leakages in seal cavity drains based on the maintenance needs of individual engines or operations. This approach is distinguishably different from the prior art which is generally based on the volume of the reservoir being primarily determined by the size of the stand pipe and geometric considerations for reducing aerodynamic drag. By individualizing the drain line cavity volume based on criticality of leakage of each individual seal, the various reservoir volumes can be maximized to realize a system reliability improvement by tailoring the maintenance need of each drain line in the system.
In yet another aspect of the present invention, there is disclosed a decentralized witness drain valve system comprised of a series of witness drain valves installed along drain lines to accurately determine the leakage amount and leakage rate at each specific drain line. Each witness drain valve incorporates a predetermined reservoir volume and a commercially available finger push valve. The system provides information on leakage amount and rate by determining, by means of the finger push valves, which reservoir has filled between consecutive inspections. The quantitative leakage assessment provides information on seal deterioration rate, and thus improves engine operational safety.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, descriptions and claims.